It may be that over time the EU develops a fully-fledged migration policy, assuming authority over the border controls of member states. The Five Presidents’ Report is concentrated on economic and monetary union. None the less, Jean-Claude Juncker referred to a “truly united, European migration policy” in his “State of the Union” address to the European Parliament last year, and an EU immigration policy already exists and there is a Common Asylum Directive. There are standardised rules on highly-qualified workers, students, unpaid trainees and researchers, as well as directives on seasonal workers and employees of multinational companies.

Most of Juncker’s speech was taken up with the migration and refugee crisis, and it makes sense for European countries to work together on it – to secure borders, process applications off-shore, tackle traffickers and gangs, co-ordinate relief, target aid on Europe’s borders, and receive refugees. ConservativeHome’s view of taking the 20,000 which David Cameron proposes to accept by 2020 was that there should be a trade-off between welcoming and integrating them (most will not return), and a commensurate reduction in immigration from elsewhere. It was sensible to take them directly from refugee camps.

And as Nick Timothy has argued on this site, there is much more that other EU countries should be doing to deal with the causes and consequences of the crisis: adopting a common approach to ISIS, spending more on defence, improving law enforcement and sharing passenger data. Above all, other European countries should be securing their internal borders, which means tearing up what is left of Schengen. However, there is a big difference between European countries working together and the EU seizing control of member states’ borders, which is why Frontex is an ambiguous development.

This takes us to the heart of the matter. I write of a common immigration policy, but there is already a common policy which makes migrant control very hard to achieve: namely, the free movement of peoples, which is a fundamental principle of the EU – stretching all the way back to the Treaty of Rome. And a leading Risk of Remain is the growing irreconcilability between free movement, the migration crisis, and British immigration control. Put simply, we are able to limit the number of people entering Britain from every country in the world except those that make up other EU member states.

Migration from them is less than half the total: roughly 270,000 people last year compared to 290,000 from outside the EU. So it would be possible to imagine that the Government might meet its net migration target were Britain to experience a slump while the Eurozone boomed, or solely by imposing further restrictions on the number of students who enter from outside the EU. But this would plainly be both an unreliable and undesirable way of reducing numbers. It would also fail to recognise that it is precisely the inter-play between free movement and the migrant crisis which threatens to make the Government’s own policy unattainable – ever.

On Juncker’s figures, 500,000 migrants made their way into Europe last year but the real number will be higher. As the Daily Telegraphhas put it, “refugees and migrants are averse to being counted, knowing that registration will impede their journey into the EU. Many cross borders by stealth, or destroy their papers to disguise their nationality”. Asylum applications in the second quarter of last year, according to Eurostate, were 85 per cent higher than during the year before. The best part of 60 per cent of those who applied in the first six months of last year were men. Most will want to work.

It is thus mistaken to claim that Britain’s benefit system is a significant pull factor for migrants (and even if it were, David Cameron’s outline deal would do little if anything to reduce it). But Britain’s economy – so healthy in comparison to that of the Eurozone – undoubtedly is. Britain’s “jobs miracle” is a magnet. So will be a growing minimum wage. And the mix of the migrant crisis and free movement is a real risk if one wants controlled immigration into the UK. Six of the 26 countries signed up to Schengen may not be operating it, but it is still in place elsewhere: in any event, those six are unused to operating full border controls and the borders of countries in mainland Europe are porous.

Furthermore, plans to scrap the Dublin Agreement, which requires claimants to seek asylum in the first safe country they come to, would have a real impact on Britain. Germany has already torn it up – which sits oddly with its exasperation with southern European countries for simply waving arrivals through to northern European ones. Theresa May briefed the Sun about her “exasperation” last week. She grasps that some of those waved on from Greece and Italy, or who make their way from eastern to western Europe, will duly seek in turn to move on to Britain and into its healthy jobs market.

The key point here is not about numbers: there is a respectable case for having higher immigration, though it is not one that this site shares. It is, rather, about control. “There is not enough Europe in this Union,” Juncker said last year, the words highlighted in bold in his text to emphasise the point. We disagree. Our European partners are failing to use even the tools they have to tackle the migration crisis, and giving more to the EU will do nothing to solve the problem. The risk that Remain will mean even more uncontrolled immigration is now so high that the only safe way of responding to it is to Leave.

The counter-case made by Remain falls mainly into a narrow part and wider one. The narrow argument is that if Britain leaves the EU, France will wave migrants on to Britain. The Calais deal between Britain and France is a bilateral one that has nothing to do with the EU. And one cannot rule out the agreement hitting trouble, whether Britain leaves the EU or not. But were France to tear up the deal and point migrants in the direction of Britain, it would simply be encouraging more of them to enter France in the first place. Inevitably, some would stay. Furthermore, Britain could, in extremis, close the Channel Tunnel altogether. Would France really encourage this self-damaging scenario?

The wider argument is that Norway and Switzerland aren’t part of the EU but have higher immigration from it than Britain. But the fallacy here is obvious: the United Kingdom is neither. On Brexit, Britain would become one of the EU’s largest export markets. Given the economic relationship between Britain and its European neighbours – plus our wider place as a member of the G7, a holder of a UN Security Council seat, and a member of NATO (in which we co-operate closely with France) – limits on free movement are surely negotiable. Migration Watch estimates that leaving the EU could reduce net immigration by 100,000 a year.

All in all, the choice is between the possibility of a wrangle over free movement if we leave and the certainty of more uncontrolled migration if we do not.